FDM Tolerances, Fit & Clearance Guide | Chatelet Mfg
FDM Tolerances, Fit & Clearance: A Production Guide
A CAD model is dimensionally perfect. A printed part isn't. This is the practical guide to what FDM actually holds, the clearance values that make parts fit the first time, and how to design critical features so they land in tolerance.
The short version: Plan around ±0.2mm or ±0.5% (whichever is greater) on as-printed FDM features, with X-Y tighter than Z. For mating parts, design clearance by fit type: press ~0.05–0.10mm interference, sliding ~0.20–0.30mm, loose ~0.40–0.60mm per side. Confirm with a test coupon, and machine critical features to tighter tolerance where the drawing demands it.
What Tolerance Actually Means Here
Tolerance is the permissible deviation between the nominal dimension in your CAD file and the measured dimension on the finished part, written as ±X mm or ±X%. Every manufacturing process has one; FDM's is wider than injection molding's and much wider than machining's — and that's fine, because most functional parts don't need micron precision. The engineering skill isn't chasing the tightest number; it's knowing which features actually need to be tight and designing the rest to FDM's comfortable range.
What FDM Holds
| Dimension type | Typical as-printed tolerance | Notes |
|---|---|---|
| General (whichever is greater) | ±0.2mm or ±0.5% | Plan the design around this floor |
| X-Y (in-plane) features | Tighter — often ±0.2–0.3mm on small features | Governed by nozzle path & calibration |
| Z (build-height) features | Looser — layer-height dependent | First-layer squish + thermal contraction |
| Large parts | Widen with size (the % term dominates) | Warp/shrink grows with footprint |
| Critical features, post-machined | Tighter — drill/ream to spec | Print undersized, finish to final size |
Representative production ranges; achievable tolerance depends on geometry, material, orientation, and machine calibration.
Clearance by Fit Type — the Table to Bookmark
For anything that mates, clearance matters more than the tolerance number itself. These are starting values per side for FDM; verify with a coupon because material and orientation shift them.
| Fit type | What it does | FDM clearance (per side) |
|---|---|---|
| Press / interference | Parts join permanently, no movement | ~0.05–0.10mm interference |
| Transition | Snug — slight clearance or slight interference | ~0.10mm |
| Sliding / clearance | Parts slide or rotate freely | ~0.20–0.30mm |
| Loose / running | Easy assembly, room for tolerance stack | ~0.40–0.60mm |
Why Orientation Changes Everything
The same hole can measure differently depending on which way it faced during printing. X-Y features are drawn by the nozzle path and hold tighter; Z features stack layer by layer and inherit first-layer effects and thermal contraction. Two consequences for your design: put critical mating features in the X-Y plane when you can, and expect holes to print slightly undersized and out-of-round — which is why we print critical bores undersized and ream them to final dimension. Orientation is reviewed against your drawing on every production part; see the DfAM guide for the full treatment.
Holding Tolerance Across a Production Run
A tolerance you hit once isn't the same as one you hold across 2,000 parts. Batch-to-batch consistency comes from process control, not luck: locked process parameters so every printer runs the part identically, first-article inspection before full-run release so you approve a real part against your drawing, and dimensional verification of critical features on request. When you evaluate any supplier, ask for a first article in your material and orientation — it's the fastest proof they can hold what your part needs.
When You Need Tighter Than FDM Gives
If a feature genuinely needs ±0.05mm — a bearing seat, a precision bore, a sealing face — don't fight FDM for it. The production answer is a hybrid part: print the body, then drill, ream, or face the critical features to final tolerance. That's routinely cheaper and faster than machining the whole part from stock, and it puts machined precision exactly where the drawing needs it while keeping FDM's speed and freedom everywhere else. If most of the part needs precision, that's a signal the part may belong in a different process — and we'll tell you.
Get Your Tolerances Reviewed
Send your CAD with the critical dimensions flagged. We'll tell you what prints as-is, what needs post-machining, and commit to a lead time — typically within one business day.
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Chatelet Manufacturing is a US-based contract manufacturer in the Orlando, Florida area, operating 85+ FDM production printers. We produce carbon fiber nylon, glass filled nylon, ASA, polycarbonate, PETG, and TPU parts from prototype through low-volume production, with turnaround as soon as one week depending on part complexity and volume.